Review of the Hobbybroadcaster AMT5000 Review

So, I was reading the latest thread bashing SSTRAN over at Hobby broadcaster, and mention was made of the AMT5000 review that DeFelice had been threatening to do for some time. I then read the review. But I needn't have bothered.

It really was just another attempted hatchet job on the company and product, continuing on from the mess that was made in the AM Transmitter Challenge.

For those that aren't familiar with the Challenge, DeFelice attempted to compare the AMT5000 with several other AM transmitters, without really understanding (self-admitted, blaming SSTRAN for not answering his questions) how to tune it. Instead of waiting, or even pulling the transmitter from the testing, he just went ahead and achieved results which didn't match those of others who have used the product.

The formal review just continues from where the Challenge left off. It appears that the same AMT5000 was used in the review - preassembled and of unknown (at least to the reader) origin and quality ( it was, of course, built from a kit).

The review, if you can call it that, focused on two major areas. One was sound quality. DeFelice (he IS Hobby broadcaster, despite the inferences that there is a large test team and lab) didn't like the fact that you can't easily switch the sound processor out of the audio path, even though you can effectively disable it. Much emphasis was placed on how it is POSSIBLE to distort the audio, as opposed to the positive aspects of having the processing at all, and how to use it correctly.

The other area of attack was the claimed Class E operation. It took several months of criticism, as well as Ermi Roos, to get to the bottom of why the transmitter may have performed sub-optimally in the Challenge. DeFelice summarizes some of the tuning issues (ignoring how he botched it on the Challenge). He then 1) criticizes the fact that you need to know the ground impedance to properly tune a Class E amplifier and then 2) spends an inordinate amount of space detailing a response from an engineer who (from the schematics) questioned the Class E operation of the transmitter. Sorry, but you can't have it both ways. It should be noted that tuning instructions for typical grounds are included in the manual.

Finally, some power output figures were published that made the transmitter look very bad. What was NOT published were output figures from other transmitters. The Challenge never published absolute power figures. ALL Part 15 transmitters will have efficiencies of less than 1 percent due to the short antennas used, regardless of the efficiency of the final stage amplification. A typical Class C stage will have an efficiency of 50 percent. So you might get output from the antenna of, say 0.5 mw. The AMT5000 has the potential, everything else being equal, to get 0.85 mw (over 85 percent efficiency). It looks puny ( which is what was intended, talked about in isolation) but it's still over 50 percent greater than the others.

And by the way, the Challenge compared field strengths, not power. The measured field strength of the tested AMT5000 was not published in the review.

One of the primary strengths of the AMT5000 is its cost (slightly over $200) compared to other premium transmitters ($700+). What is laughable is that DeFelice considered it's price 'premium'.

By the end of the review (if people got that far), after pages of negatives, I guess DeFelice realized that he might be perceived as being biased (gee, you think?) - his scorecard certainly didn't reflect the overall tone of the review.

It's difficult to say why DeFelice appears to have something against SSTRAN. It seems to be personal to some extent. Perhaps it's the less than enthusiastic response to his demands (a test transmitter) and questions. Although I've noticed the negative attitude from well before the Challenge.

It just goes to show that you can't always believe everything you read, even from sources that are normally reputable. You also need to understand the biases of the author.